TORSIONAL TESTING OF THE LIGHTSPEED NICKEL-TITANIUM INSTRUMENT SYSTEM

Revolutions to separation and maximum torque at failure of 216 Lightsp eed instruments were determined in an Instron using a clockwise rotati on, After instruments failed, the distance the instrument separated fr om the tip was measured, Comparison of the results with existing ANSI/ ADA specification no, 28 showed that the Lightspeed far exceeded the v alues of the specification for revolution to failure, On the other han d, torque to failure results showed that instrument sizes 20 and 25 ex ceeded the specification, whereas instrument sizes 30 through 50 were below the minimum values, Half-size instruments were not compared, bec ause specifications for half-sizes do not exist, Comparison between me an torque values and instrument shaft diameters of the Lightspeed prev iously reported showed a near linear relationship up to and including instrument size 50, but overall torque to failure increased exponentia lly when related to shaft diameter (coefficient of determination = 0.9 923), Lightspeed instruments separated 2.32 +/- 0.60 mm from the tip, generally within the land area or at the beginning of the shaft, Scann ing electron microscopic observation of the Lightspeed instrument frac ture site showed two distinct areas, There was a striated concentric a rea in the periphery of the fracture characteristic of a brittle or cl eavage fracture and a corrugated area in the center of the fracture ch aracteristic of a ductile fracture.